1. Field of the Invention
This invention relates to electronic devices for power amplification and more particularly to audio signal amplification. The new device provides for a combination of at least three selectable amplifier channels in a single integrated circuit package to allow use as a one, two or three channel amplifier device with varying output power based on the mode selected.
2. Description of Related Art
Use of independent amplifiers, basically in two channel configurations such as found in stereo systems, to form a bridging two channel amplifier are known in the art. This type of circuit for use in audio systems has often been used. This is particularly true in audio systems where power supply limitations exist and where inexpensive circuitry is desired yet a more powerful audio sound output is needed.
More recently such two channel bridging circuit have been used with computer sound cards. In these applications the computer sound card amplifying capabilities are limited by the computer power management scheme. In such instances the computer sound card amplifier is bridged with an external audio amplifier to power a speaker. By properly selecting and balancing the components the bridging circuit configuration can approximately double the speaker power output as for example as described in U.S. Pat. No. 5,586,194.
Use of independent and bridged power amplifiers includes development of devices with paired amplifiers which may be switched by external control from independent operation for stereo operation to bridged operation for increased single speaker output audio power. By proper design of integrated circuit elements a device which uses the same minimum connecting pin leads as existing two channel independent operation devices has been formulated.
More modernly the need for additional audio output power in the limited computer supply power environment has been created by the development of computer multimedia devices such as CD-ROM and DVD players. These computer multimedia devices provide quality grade audio music if they are coupled with an adequate audio power and speaker system.
The present invention includes a three channel signal amplifier in a single package which may be used in a three channel audio power amplifier to support for example surrounding sound effect speaker systems which require three independent amplifier channels. The integrated circuit device contains control circuitry to allow use of the device in the 3 channel mode or in 2 channel and 1 channel modes to provide increased output power to fewer speakers.
The typical class A or class AB operation amplifier can only normally achieve efficiencies of less than 60% on average. Therefore in the instant invention class D operation amplifiers are implemented which are balance bridge connected and transformer coupled to the output load or speakers. In this configuration the class D amplifier can theoretically achieve more than 85% efficiency.